1. Technical Field
The invention relates to the field of gas generators, and more particularly to an electronic control for a pressure swing adsorption apparatus.
2. Background Art
There are a wide variety of applications in which oxygen or another desired product gas is required.
On Board Inert Gas Generating Systems (OBIGGS), or On Board Oxygen Generating Systems (OBOGS) utilize molecular sieves by employing a pressure swing adsorption (PSA) process that has been used for many years to generate either Nitrogen or Oxygen product gas respectively. This known PSA technology uses compressed air or conditioned engine bleed air fed through a valve or valves to pressurize molecular sieves contained in one of a number of canisters. After a predetermined period of time, the valve changes state, venting the one canister full of sieve, then pressurizing the next canister. This process of pressurization and venting is the PSA process. Known PSA systems have been controlled by a rotary valve, driven by a fixed or variable speed motor. Still others utilize a system of dedicated independent valves to control each pressurization and each venting cycle for each canister or bed.
Prior PSA systems have also utilized a linear 4-way slide valve, which connects input air port with the first canister, while connecting a vent port with the second canister. The valve changes state, which connects the vent port with the first canister and simultaneously connecting the second canister with the input air. The linear 4-way slide valve simplifies the complex system of independent dedicated valves necessary on some systems. The linear valve has also proven to be more reliable then either the rotary valve or the system of valves, accomplishing the same tasks.
The linear valve used on typical PSA systems is pneumatically operated. Miniature pilot solenoid valves that are opened and closed using solid state electronics, housed in an EMI shielded enclosure control pilot gas. The pilot solenoids provide gas pressure to two gas cylinders, which are connected to a sliding block. The block slides across a mating plate with three openings or ports. A controller is set to open and close the miniature pilot valves at a predetermined time.
In some applications, the source of new air is limited. Many airborne and ground based systems have a finite source of air. There are many uses for bleed air on rotary and fixed wing aircraft, hence conserving the available air is critical. There have been a number of studies conducted for various concepts for air conservation. A number of these studies have resulted in patents, such as U.S. Pat. Nos. 5,858,063, 6,409,807, and 5,074,893.
Numerous other U.S. patents, such as U.S. Pat. Nos. 5,766,310, and 6,063,169 as examples, teach oxygen concentrating systems using molecular sieve bed units having two or more molecular sieve beds comprising a molecular sieve oxygen generator. The disclosures of which referenced patents are hereby incorporated in their entirety as if fully set out herein.
PSA type gas concentrators generally present a varying pneumatic load to their air source. Through the course of the PSA cycle the peak airflow drawn from the air source by a concentrator can vary from nearly zero to 3 times the average flow. The peak airflow capability of most air supplies is limited by several factors, such as: compressor capacity, piping diameter and length, presence of additional storage volume, etc. When several PSA concentrators are connected to the same air source, it is desirable to control the phasing of the individual concentrator cycles to minimize the peak airflow demands on the air source. The following graph of FIG. 2 illustrates a typical input airflow versus time for a known PSA concentrator.
It can be seen from FIG. 2 that if the phasing of several concentrator cycles becomes synchronized, or nearly so, the peak airflow demands on the air supply will be increased significantly. In extreme cases the airflow demand may exceed the capability of the air supply and the operating efficiency of the concentrators will be reduced.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.